In many conversion processes, reactants are mixed to obtain a gaseous mixture that is contacted with a catalyst bed. For optimal mixing, it is advantageous to use a mixing zone with a relatively large ratio of length to diameter. Therefore, the cross-sectional area of the mixing zone is generally smaller than that of the catalyst bed with which the mixture is to be contacted. In order to distribute the mixture evenly over the upstream surface of the catalyst bed, either a plurality of mixers can be used or the mixture has to be spread over the upstream surface of the catalyst bed.
If the reactants form a mixture that is susceptible to ignition or explosion, such as is the case in processes for oxidation of a hydrocarbonaceous fuel wherein a mixture of hydrocarbonaceous fuel and a molecular oxygen containing gas is contacted with a catalyst, it is important that variations in the residence time of the mixture in the zone upstream of the catalyst are minimal. Zones wherein the flow of the feed mixture is stagnant are to be avoided. Reference herein to zones wherein the flow is stagnant is to zones wherein the residence time of the mixture is relatively long as compared to the average residence time of the mixture.
In EP 303 439, a gas mixer and distributor for feeding a gaseous reaction mixture to a catalytic partial oxidation reaction zone is disclosed. The disclosed gas mixer and distributor comprises a plurality of small mixing tubes opening above a larger catalytic reaction zone.
In WO 98/49095 is disclosed an injector/reactor apparatus for the catalytic partial oxidation of light hydrocarbons comprising a manifold of mixing nozzles upstream of a larger catalytic partial oxidation zone.
In WO 98/30322, a catalytic reactor for partial oxidation of a hydrocarbonaceous feedstock comprising a mixer-diffuser for mixing a hydrocarbonaceous feedstock and an oxygen-containing gas and subsequently spreading it over the catalyst surface is disclosed. In the disclosed mixer-diffuser, the mixture is first expanded in an annular chamber by increasing the diameter of the annular flow path of the mixture without increasing the available cross-sectional area of the flow path, the expanded mixture is then supplied via an annular inlet to a distribution chamber. A disadvantage of the mixer-diffuser of WO 98/30322 is that the mixture is axially supplied to the expander/diffuser, thereby requiring a relatively high mixing chamber.